The present invention relates to a power transmission apparatus and, more particularly, to a power transmission apparatus having a torque limiter mechanism such as a compressor for an automobile air conditioner.
As a conventional power transmission apparatus of this type, for example, one described in Japanese Utility Model Publication No. 6-39105 is known. In the power transmission apparatus described in this reference, fitting holes are formed in axially opposing side surfaces of the pulley (driving rotary member) of a compressor (driven device) and a hub (driven rotary member) mounted on the rotating shaft of the compressor. A connecting member comprised of a member that can be broken upon application of an overload is press-fitted in these fitting holes to form a torque limiter mechanism. When an overload acts on the rotating shaft, a power from a vehicle engine (driving device) breaks the connecting member.
In the conventional power transmission apparatus described above, the connecting member is broken when an overload is temporarily applied to the rotating shaft due to some reason. The compressor cannot be driven again unless the connecting member is exchanged for a new one.
In order to solve the above problem, a power transmission apparatus disclosed in, e.g., EP 0864454 A2 is proposed. In this power transmission apparatus, a washer is interposed between an inner holding member and an arc-shaped projection formed on the flange of a hub. When the inner holding member is pressed by a coned disc spring through another washer, the inner holding member is connected to the two washers through frictional engagement. When an overload is applied, the hub washer is moved into a recess formed in the arc-shaped projection to displace the inner holding member toward the hub, so that frictional engagement is canceled. Therefore, power transmission can be disconnected in a nondestructive manner.
In the power transmission apparatus disclosed in EP 0864454 A2 described above, after power transmission is disconnected, the flange of the inner holding member, the arc-shaped projection of the hub, and the washers slide on each other. Due to this structure, a drag torque may be generated, or a sliding noise and friction heat may be easily generated. In particular, when friction heat is generated, it degrades a rubber member connecting the outer and inner holding members to each other. When frictional engagement is canceled and power transmission is disconnected, the inner holding member and the washers become movable in the axial direction. Then, when the inner holding member and the washers are moved by vibration or the like, noise is produced.